package 树;

import java.util.*;

public class _101_对称二叉树 {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;
        return dfs(root.left,root.right);
    }

    private boolean dfs(TreeNode left, TreeNode right) {
        if (left == null && right == null) {
            return true;
        }
        if (left == null || right == null) {
            return false;
        }
        if (left.val != right.val) {
            return false;
        }
        return dfs(left.left,right.right) && dfs(left.right,right.left);
    }
}
